Optical fiber coupling unit and optical waveguide arrangement, and method of producing an optical fiber coupling unit

ABSTRACT

Optical fiber coupling unit and optical waveguide arrangement, and method of producing an optical fiber coupling unit. The optical fiber coupling unit  1  has: an optical fiber  2 , which has a fiber core  4  and a fiber cladding  6  surrounding the fiber core  4 , and a sleeve  8 , which is arranged on an end portion of the optical fiber  2  and terminates flush with the associated extreme end  14  of the optical fiber  2 , so that on this extreme end  14  there is formed a continuous coupling face  16 , with which the optical fiber coupling unit  1  can be placed against an optical waveguide component to establish an optical coupling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 ofGerman Patent Application No. 101 03 125.4 filed on Jan. 24, 2001.

FIELD OF THE INVENTION

The invention relates to an optical fiber coupling unit for coupling anoptical fiber to an optical waveguide component, in particular to aplanar optical waveguide component, such as an optical chip for example.The invention also relates to an optical waveguide arrangement and amethod of producing an optical fiber coupling unit.

BACKGROUND OF THE INVENTION

For coupling optical fibers, for example glass fibers, to an opticalchip, on which optical structures are provided, today the optical fibersare usually bonded onto the chip by means of an adhesive. When doing so,the optical fibers are generally bonded with their front-end faces ontoan associated end face of the chip.

A typical optical fiber contains a fiber core and a fiber claddingsurrounding the fiber core, which together form the actual light guide.To protect the optical fiber, it, i.e. the arrangement comprising thefiber core and fiber cladding, is usually provided with a sheathing, forexample in the form of a coating applied directly to the fiber cladding.The coating typically consists of plastic. The sheathing may,furthermore, have an additional outer layer, for example the coating maybe additionally buffered with a resistant flexible material, as alsoused for cables.

The outside diameter of a standard single-mode glass fiber with a fibercore and fiber cladding, that is without the sheathing, is typically 125μm. The resulting end face of the individual optical fiber is notsufficient in this case to achieve a stable and reliable adhesive bondbetween the end face of the optical fiber and the chip.

In the case of a known coupling unit for coupling one or more opticalfibers, what is known as a fiber array is adhesively bonded onto theoptical chip to achieve a stable and reliable bond.

FIG. 1 shows such a fiber array 101 according to the prior art in a viewfrom the front. The fiber array 101 is made up of a base plate 103, aV-groove platelet 104, in which a plurality of V grooves 105 arranged ata distance from one another and running parallel to one another havebeen formed, and a plurality of optical fibers 106, which have been laidin the associated V grooves 105. In this case, generally the opticalfibers 106 are first laid in the V grooves 105. Then, the V-grooveplatelet 104 together with the optical fibers 106 and the base plate 103are bonded together, whereby the optical fibers 106 are fixed in the Vgrooves 105. The end face 107 of the arrangement comprising the V-grooveplatelet 104 together with the optical fibers 106 and base plate 103 issubsequently ground and polished, so that a planar coupling face iscreated for bonding the fiber array 101 onto a chip. As can be seen fromFIG. 2, the fiber array 101 is attached by this coupling face to theassociated extreme end of an optical chip 108 to establish an opticalcoupling.

To ensure a precise and controlled coupling of the optical fibers 106onto the chip 108, the V-groove platelet 104 must be fabricated veryaccurately. The fabrication of V-groove platelets with sufficiently highprecision is achieved for example by etching. However, because of thesmall dimensions of the V grooves 105, this fabrication is complex.

SUMMARY OF THE INVENTION

The invention provides an optical fiber coupling unit for a opticalfiber, by means of which coupling unit the optical fiber can beoptically coupled to an optical waveguide component in a reliable way,and which has a simple construction and can consequently be realized atlow cost. The invention also provides a method of producing an opticalfiber coupling unit, with which the optical fiber coupling unitaccording to the invention can be precisely produced in a simple way.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a fiber array according to the prior art in a view from thefront,

FIG. 2 shows the fiber array from FIG. 1 in plan view, with its couplingface coupled onto an optical chip,

FIG. 3a shows an embodiment of the optical fiber coupling unit accordingto the invention in longitudinal section,

FIG. 3b shows the optical fiber coupling unit from FIG. 3a in a viewfrom the front,

FIG. 4a shows a schematic partial view of another embodiment of theoptical fiber coupling unit according to the invention in longitudinalsection,

FIG. 4b schematically shows the optical fiber coupling unit from FIG. 4ain a cross section along the line 4 b-4 b,

FIG. 5a shows another embodiment of the optical fiber coupling unitaccording to the invention in longitudinal section,

FIG. 5b shows the optical fiber coupling unit from FIG. 5a in a viewfrom the front,

FIG. 6a shows another embodiment of the optical fiber coupling unitaccording to the invention in longitudinal section,

FIG. 6b shows the optical fiber coupling unit from FIG. 6a in crosssection along the line designated in FIG. 6a by 6 b-6 b,

FIG. 7a shows another embodiment of the optical fiber coupling unitaccording to the invention in longitudinal section,

FIG. 7b shows the optical fiber coupling unit from FIG. 7a in a viewfrom the front, and

FIG. 8 schematically shows an optical waveguide arrangement according toone embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The optical fiber coupling unit according to the invention has: anoptical fiber and a sleeve, which is arranged on an end portion of theoptical fiber and terminates flush with the extreme end, i.e. flush withthe associated end face, of the optical fiber, so that on this extremeend there is formed a continuous coupling face, with which the opticalfiber coupling unit can be placed onto an optical waveguide component toestablish an optical coupling.

The coupling face jointly formed by the optical fiber and the sleeveforms a sufficiently large placement face for placing and bonding ontoan optical component, such as an optical chip for example, so that areliable mechanical, and consequently ultimately optical, coupling isachieved between the optical fiber and the optical component. The sleeveis formed in particular as a circumferentially closed sleeve andconsequently extends preferably uninterruptedly around the opticalfiber. The sleeve for its part represents a component which is simple toproduce; it is envisaged here in particular to use already existingstandard components, such as ferrules in particular, as sleeves.

The inside diameter of the outer sleeve is preferably not much greaterthan the outside diameter of the optical fiber, so that the sleeverepresents in particular a capillary. The optical fiber isadvantageously closely surrounded by the sleeve, in particular with adistance between the optical fiber and the inner wall of the sleeve of1-5 μm. That is to say that the inside diameter of the sleeve ispreferably approximately 2 to 10 μm greater than the outside diameter ofthe optical fiber accommodated in it.

The close fit thereby achieved on the one hand fixes the optical fiberin the sleeve. On the other hand, it prevents the optical fiber fromassuming a skewed position in the sleeve and/or experiencing bends orkinks, whereby the attenuation of the optical fiber for light passedthrough would be increased.

However, depending on the accuracy requirement, the inside diameter ofthe sleeve may also be considerably greater, i.e. for example more than10 μm, than the outside diameter of the optical fiber, so that theoptical fiber can be inserted with sufficient play in the sleeve. In anyevent, the intermediate space between the optical fiber and the sleeveis preferably filled with a filling material, for example hot-meltadhesive, by which the optical fiber and the sleeve are fixed againsteach other.

The optical fiber is preferably bonded into the sleeve by means ofadhesive. This takes place in particular by the optical fiber beingprovided laterally on its end portion with the adhesive agent andsubsequently inserted into the sleeve. That is to say the adhesive agentis provided in particular lengthwise between the optical fiber and thesleeve.

The coupling face may extend perpendicularly with respect to thelongitudinal axis of the optical fiber. However, the coupling face ispreferably beveled, thereby avoiding partial reflection back into theoptical fiber at the coupling face of light emerging from the opticalfiber at the coupling face. The coupling face is preferably beveled hereat an angle of 8 degrees, so that the coupling face is consequentlyinclined at an angle of 82 degrees with respect to the longitudinal axisof the optical fiber.

The sleeve may in principle be made of any desired material which issufficiently solid to allow the optical fiber to be held and reliablyattached, in particular bonded, to the optical waveguide component. Thesleeve is preferably made of a material which has the same, orsubstantially the same, coefficient of thermal expansion as the opticalfiber material. Since the optical fibers are made in particular of aglass material, the sleeve is consequently preferably made of a glassmaterial or a ceramic material.

A commercially available glass capillary may be used as the sleeve.Capillaries of this type are generally circular-cylindrical tubes with acircular-cylindrical bore. They are commercially available inexpensivelyin a wide variety of dimensions and nevertheless have a sufficientlyhigh fabrication accuracy for the invention.

As explained above, a ferrule obtainable in telecommunications isparticularly envisaged as the sleeve. Ferrules are tubular elementswhich are standardized in connector technology and are available inparticular in the form of glass or ceramic ferrules. They are typicallycircular-cylindrical with a circular-cylindrical bore and have a highfabrication accuracy, while they are nevertheless inexpensive. Forexample, ferrules with an inside diameter of 127 μm are offered with afabrication tolerance in this respect of +1 μm. Such a ferrule isconsequently well-suited according to the invention for an optical fiberwith an outside diameter of 125 μm.

The sleeve preferably has an outside diameter of at least 2 mm, inparticular of 2 mm to at most 10 mm. With these outside diameters, asufficiently large coupling face is attained to achieve a reliable andpermanent adhesive bond between the coupling face and a placement faceon an optical waveguide component, on which placement face the opticalfiber coupling unit is placed with its coupling face. The outsidediameter is also to be regarded here as the peripheral diameter of anon-circular coupling face in the case for example of across-sectionally non-circular sleeve. Greater outside diameters arepossible in principle, but generally not advantageous because of theexcessive space requirement.

Like the conventional ferrule for example, the sleeve preferably has acylindrical, in particular circular-cylindrical, outer shape and isprovided with a cylindrical, in particular circular-cylindrical,through-bore, which extends in its longitudinal direction and throughwhich the optical fiber extends.

The sleeve preferably has a planar surface on its periphery. Such aplanar surface may be produced in the case of a circular-cylindricalsleeve by circumferential grinding for example. The planar surfaceserves as a face for placing onto a planar alignment face assigned toit, which is provided for example on the optical waveguide component oron a fitting aid. That is to say the sleeve is placed with its planarouter surface on the alignment face, whereby the sleeve and consequentlythe optical fiber arranged in it are aligned with respect to theircircumferential direction. This allows it to be optically coupledexactly to a correspondingly aligned optical waveguide component, justby it then being pushed axially up to said component. The provision of aplanar surface on the circumference of the sleeve is of advantage inparticular if the coupling face and the placement face assigned to it onthe optical waveguide component, such as the end face of an optical chipfor example, are beveled. In this case, the placement face is ground atthe same angle as the end face of the optical fiber coupling unit, sothat the optical fiber coupling unit can be placed with its couplingface flat against the placement face of the optical waveguide component.The planar surface on the sleeve facilitates here the correct alignmentof the mutually opposed sloping faces, that is to say the coupling faceand the placement face.

The planar surface may be provided at any desired location on thecircumferential surface of the sleeve. A plurality of planar surfacesmay also be provided, for example a planar surface on opposite sides ofthe sleeve, so that the sleeve is bounded in cross section by straightlines lying opposite each other, in particular parallel to each other,and two arc-of-a-circle segments lying in between.

The planar surface is preferably provided alongside the coupling faceand, furthermore, preferably extends up to the coupling face.Consequently, the optical fiber coupling unit can be placed with itsplanar surface at the extreme end against a planar alignment faceassigned to the latter.

The sleeve is preferably made of a material which has a coefficient ofthermal expansion substantially corresponding to that of the opticalfiber. As a result, thermal stresses between the optical fiber and thesleeve are avoided.

In the event that the optical fiber, which has a fiber core and a fibercladding surrounding the latter, is provided with a sheathing, which isformed for example by a coating applied directly to the optical fiberand a buffer arranged over that (conductor with insulating sheathing),the optical fiber can be inserted together with its sheathing into thesleeve. The sleeve in this case preferably has an inside diameter whichis 2 to 10 μm greater than the outside diameter of the covered opticalfiber, i.e. 2 to 10 μm greater than the outside diameter of thesheathing.

For the reason mentioned above, i.e. to avoid thermal stresses betweenthe optical fiber and the sheathing, which is generally not made of alight-conducting material, a coating which may be present on the opticalfiber, and is made of plastic for example, and a buffer which may besurrounding the coating (conductor with insulating sheathing) areremoved toward the extreme end of the optical fiber, so that the opticalfiber extends out of the sheathing with an exposed end portion, on whichthe sleeve is arranged. Consequently, in the end portion of the opticalfiber, the sleeve is preferably arranged directly on the optical fiber,that is to say with the exception of the adhesive arranged in between.

The sheathing may be arranged, for example, with its extreme end upagainst the sleeve or at least alongside it. According to a preferredembodiment of the invention, the sleeve extends with an end portionremote from the extreme end of the optical fiber over the sheathing, thelatter being accommodated snugly in the sleeve in an advantageous way.As a result, the optical fiber is protected even better againstbuckling, since that location at which the sheathing is detached fromthe optical fiber is not exposed but is covered by the sleeve.Furthermore, forces present in the sheathing are also at least partiallyabsorbed by the sleeve portion extending part way over the sheathing,thereby ultimately relieving the optical fiber.

The inside diameter of the rear sleeve portion, which is remote from theextreme end of the optical fiber to be coupled onto the opticalwaveguide component, is preferably 2 to 10 μm greater than the outsidediameter of the sheathing. That is to say the distance between thesheathing and the associated inner wall of the sleeve is preferably 1 to5 μm. The sleeve is preferably solidly bonded to the sheathing, inparticular by means of an adhesive agent, so that the optical fiber isrelieved of tension, since tensile forces are introduced from thesheathing into the sleeve via this bond.

The optical fiber coupling unit according to the invention can beproduced in the following way:

According to one possible method, firstly the sleeve and the opticalfiber are individually ground and/or polished on one of their extremeends, thereby forming a planar end face, in particular in such a waythat the respective end face is formed as a sloping face and preferablyruns at an angle of 82 degrees with respect to the longitudinal axis ofthe sleeve or fiber. Subsequently, the sleeve is pushed, with its endremote from the sloping face in front, over the optical fiber. Afterthat, the sleeve and the optical fiber are aligned with their faces atthe extreme ends, in particular sloping faces, flush with respect to oneanother, so that the continuous, stepless coupling face is formed at theextreme ends.

According to the preferred method according to the invention forproducing the optical fiber coupling unit according to the invention, asleeve is pushed onto an end portion of an optical fiber and fastened tothe optical fiber. In this case, the sleeve is advantageously pushedover the optical fiber to the extent that the latter protrudes with itsfree end out of the sleeve by approximately 2-3 mm. Before the sleeve ispushed onto the optical fiber, the latter is preferably providedlaterally, or the sleeve is provided on its inner side, with an adhesiveagent, which provides an adhesive bond between the optical fiber and thesleeve. Subsequently, the sleeve with the optical fiber accommodated init is ground and/or polished at the extreme end, thereby forming acontinuous, i.e. stepless, coupling face at the extreme end. Thegrinding and/or polishing may be performed in such a way that thecoupling face is formed as a sloping face and runs in particular at anangle of approximately 82 degrees with respect to the longitudinal axisof the optical fiber (and the sleeve).

In the case of this method, a planar, i.e. stepless, coupling face isobtained in a simple and consequently low-cost way. The fastening of theoptical fiber in the sleeve is preferably performed by means of bondingthe optical fiber into the sleeve.

The optical fiber is preferably bonded by being wetted with an adhesivebefore it is inserted into the sleeve, said adhesive filling theintermediate space between the sleeve and the optical fiber after it hasbeen inserted.

Alternatively, the sleeve may first be completely filled with adhesiveand the optical fiber subsequently inserted into the sleeve, part of theadhesive being forced out of the sleeve again.

In the case of a two-part sleeve with an inner sleeve and an outersleeve, the optical fiber is first inserted into the inner sleeve andbonded to the latter, in particular in the way described above.Subsequently, the outer sleeve is pushed over the inner sleeve and thesheathing and fixed on the inner sleeve and the sheathing by means of anadhesive bond. Finally, the planar coupling face is produced by grindingand/or polishing.

The optical waveguide arrangement according to the invention has anoptical waveguide component, in particular an optical chip, which has aplacement face, in particular a planar placement face, from which anoptical structure extends, and also an optical fiber coupling unitaccording to the invention, which is placed with its coupling faceagainst the placement face of the optical waveguide component, therebyestablishing optical coupling between the optical fiber and the opticalstructure, and is fastened on said placement face, preferably by meansof an adhesive bond.

Preferred embodiments of the invention are described below withreference to the drawings.

In the drawings, the same designations are used for the same parts.

FIG. 3a shows an optical fiber coupling unit 1 according to oneembodiment of the invention in longitudinal section.

The optical fiber coupling unit 1 shown in FIG. 3a has an elongateoptical fiber 2 with a fiber core 4 and a fiber cladding 6, surroundingthe fiber core 4, and also an elongate sleeve 8 in the form of acapillary.

FIG. 3b shows the optical fiber coupling unit 1 according to FIG. 3a ina view from the front, i.e. the optical fiber coupling unit 1 accordingto FIG. 3a from the right. The optical fiber 2 and the sleeve 8 have acircular outer cross section.

A standard single-mode glass fiber with an outside diameter, i.e. afiber cladding diameter, of 125 μm may be used as the optical fiber 2. Aglass capillary with an outside diameter of 3 mm, an inside diameter of128 μm+2 μm tolerance and a length of at least 2 to 10 mm is, forexample, provided as the sleeve 8. The intermediate space between theoptical fiber 2 and the sleeve 8 is filled with an adhesive.

The optical fiber 2 protrudes with an exposed, front end portion 10 outof a sheathing 12, by which it is otherwise surrounded. The opticalfiber 2 and the sheathing 12 surrounding it form a fiber-optic cable 13or a stranded wire of a multi-stranded-wire fiber-optic cable. Thesleeve 8 is arranged on this exposed end portion 10 of the optical fiber2 and terminates at the front flush with the extreme end 14 of theoptical fiber 2, so that at this extreme end 14 a continuous, i.e.extending over the extreme end 14 of the optical fiber 2 and the extremeend of the sleeve 8, planar coupling face 16 is formed, with which thecoupling unit 1 can be placed against an optical waveguide component,for example an optical chip, or else another coupling unit, in order inthis way to establish an optical coupling of the optical fiber 2 withthe optical waveguide of the optical waveguide component. The couplingface 16 runs perpendicularly with respect to the longitudinal axis ofthe cylindrical optical fiber 2 and the cylindrical sleeve 8.

The sheathing 12 consists of a plastic coating resting directly on thefiber cladding and a buffer surrounding the coating, known as theconductor with insulating sheathing. In the region of the sleeve 8, theoptical fiber 2 has been freed of the sheathing 12, thereby forming saidexposed portion 10.

FIG. 4a schematically shows a partial view of another embodiment of theoptical fiber coupling unit 1 according to the invention in longitudinalsection. FIG. 4b shows the optical fiber coupling unit 1 from FIG. 4a incross section along the line 4 b-4 b in FIG. 4a.

The optical fiber coupling unit 1 from FIG. 4a corresponds substantiallyto that coupling unit 1 described on the basis of FIGS. 3a and 3 b;however, in comparison with the optical fiber coupling unit 1 from FIGS.3a, 3 b, it has a coupling face 16 beveled at an angle α of 8 degrees(FIG. 4a), that is to say 8 degrees with respect to a coupling faceperpendicular to the longitudinal axis of the fiber or 82 degrees withrespect to the longitudinal axis of the fiber.

If the optical fiber coupling unit 1 according to the embodiment fromFIGS. 4a, 4 b is coupled onto an optical chip, the chip is beveled at aplacement face, against which the optical fiber coupling unit 1 isplaced with its coupling face 16, in such a way that it matches thecoupling face 16 of the optical fiber coupling unit 1 at an angle of 8degrees in the same direction, so that the coupling face 16 and theplacement face can be placed flat against each other when the opticalwaveguides (optical fiber 2 and light guiding structure of the chip) arealigned such that they are in line with each other. The fact that thesleeve 8 terminates flush with the extreme end 14 of the optical fiber 2has the effect that the coupling face 16 extends continuously, i.e. in astepless and consequently planar manner, over the extreme end of theoptical fiber 2 and the sleeve 8. That is to say both the end face ofthe sleeve 8 and the end faces of the fiber core 4 and the fibercladding 6 of the optical fiber are beveled at the angle α.

It can be seen from FIG. 4b that the sleeve 4 has on its circumferentialsurface a flattened portion in the form of a planar surface 18. Theplanar surface 18 makes it easier to align the optical fiber couplingunit 1 correctly in the rotational direction about its longitudinal axiswhen it is being coupled onto an optical waveguide component, such asthe optical chip. This allows the coupling face 16, provided as asloping face, to be placed more easily in such a way that it fitsagainst the placement face assigned to it, likewise formed as a slopingface, on the optical waveguide component, which for this purpose has forexample a likewise planar alignment face, against which the couplingunit 1 can be placed by its planar circumferential surface 18, therebyaligning its coupling face 16 with respect to the placement face.However, the optical waveguide component and the optical fiber couplingunit 1 may also be placed with their aligning face or their planarcircumferential surface 18 onto a separate, planar aligning part and,guided by this, in particular also additionally laterally guided, beplaced with their extreme ends against each other.

FIG. 5a shows another embodiment of the optical fiber coupling unit 1according to the invention in longitudinal section. In the case of thisembodiment, a fiber-optic cable 13 is provided with an optical fiber 2and a sheathing 12, by which the optical fiber 2 is surrounded. Theoptical fiber 2 is freed in its end portion 10, on the right in FIG. 5a,of the sheathing 12 toward the associated extreme end 14, so that thisend portion 10 of the optical fiber 2 represents an exposed portion.

The exposed end portion 10 of the optical fiber 2 is closely surroundedby a circular-cylindrical, closed sleeve 8, which terminates flush withthe end face of the optical fiber 2, thereby forming a continuouscoupling face 16 at the extreme end.

The sleeve 8 extends from the extreme end 14 of the optical fiber 2 witha rear sleeve portion 20 over the sheathing 12 and closely encloses thelatter. The sheathing 12 is solidly bonded here to the sleeve 8 by meansof adhesive; the exposed end portion 10 of the optical fiber 2 is alsobonded by means of adhesive into the associated front sleeve portion 22.

The sheathing 12 may be formed by a coating applied directly to theoptical fiber 2 and a buffer surrounding said coating. In this case, itmay also be provided that the coating extends with an exposed endportion out of the buffer, only the exclusively coated part of theoptical fiber 2 being surrounded by the sleeve 8, that is to say by itsrear sleeve portion 20, whereas the buffer is detached in front of theend of the sleeve 8 on the left in FIG. 5a.

The overlapping of the sleeve 8 and sheathing 12 has the effect that theoptical fiber 2 is protected from outside influences, and in particularfrom buckling, at that location at which the sheathing 12 is detached.In particular, tensile forces present in the fiber-optic cable 13 can bepassed on from the sheathing 12 via the adhesive bond to the sleeve 8and absorbed by the latter. As a result, the optical fiber 2 is relievedof tension.

According to one embodiment of the invention, the optical fiber 2 has adiameter of 125 μm; this is the case in particular with a standardsingle-mode fiber. The fiber-optic cable 13 comprising the optical fiber2 and the sheathing 12 here has in particular a diameter of 900 μm. Inthis case, the sleeve 8 preferably has in its front sleeve portion 22,i.e. its portion toward the extreme end 14 of the optical fiber 2 to becoupled, by which portion the associated, exposed end portion 10 of theoptical fiber 2 is surrounded, an inside diameter of approximately 128μm and in its rear portion 20, i.e. its portion remote from the extremeend 14 of the optical fiber 2 to be coupled, by which portion theassociated portion of the optical fiber 2 not freed of the sheathing 12is surrounded, an inside diameter of 903 μm.

The sleeve 8 may be a part made of a single material, in which twocentral longitudinal bores of different diameters in line with eachother are provided for receiving the exposed optical fiber portion 10and the optical fiber portion sheathed by the sheathing 12. The sleevemay, however, also be made up of two separate sleeve parts, the frontsleeve portion 22 being formed by a first sleeve part and the rearsleeve portion 22 being formed by a second sleeve part, the sleeve partsbeing placed against each other and solidly joined together at theextreme ends, for example by means of adhesive bonding, thereby formingthe sleeve 8.

FIG. 5b shows the optical fiber coupling unit 1 from FIG. 5a in a viewfrom the front, i.e. from the right in FIG. 5a, so that the sleeve 8 andthe optical fiber 2 inserted in it and also the associated coupling face16 can be seen.

Another embodiment of the invention, which represents a variant of theembodiment shown in FIGS. 5a, 5 b, is shown in FIGS. 6a, 6 b. FIG. 6ashows here a longitudinal section of the optical fiber coupling unit 1according to the invention, and FIG. 6b shows the optical fiber couplingunit 1 in a cross section along the line designated by 6 b-6 b in FIG.6a.

As can be seen from FIG. 6a, the sleeve 8 according to this embodiment,like the sleeve 8 according to FIGS. 5a and 5 b, is designed in such away that it extends with a rear sleeve portion 20, remote from theextreme end 14 of the optical fiber 2 to be coupled, over the sheathing12 of the optical fiber 2. By contrast with the sleeve 8 according toFIGS. 5a and 5 b, however, the rear sleeve portion 20 is not providedlike the front sleeve portion 22 as a closed sleeve part. Instead, thesleeve 8 is provided in its rear sleeve portion 20, remote from theextreme end 14, with a central transverse slit 24, which is continuousin the direction of the diameter of the sleeve 8 and extends over theentire axial length of the rear sleeve portion 20, which for its partmakes up approximately half the axial length of the sleeve 8. Thetransverse slit 24 has a width w (see FIG. 6b), which is slightlygreater, in particular 2 to 10 μm greater, than the outside diameter ofthe sheathing 12, so that the transverse slit 24 forms a slit space 26,in which the optical fiber 2 is accommodated together with its sheathing12 in such a way that it is virtually free from play on two sides. Ifthe aforementioned sheathing 12 with an outside diameter of 900 μm isused, the transverse slit 24 preferably has a width w of 903 μm. Thelateral fixing of the sheathed optical fiber 2 in a direction parallelto the slit walls is achieved in particular by the optical fiber 2 withsheathing 12 being bonded into the slit space 26.

The embodiment according to FIGS. 6a, 6 b has the advantage that atransverse slit 24 of a width w in the μm range can be produced moreeasily than an axial bore with a diameter likewise in the μm range.

FIG. 7a shows another embodiment of the optical fiber coupling unit 1according to the invention in longitudinal section.

The optical fiber coupling unit 1 according to this embodiment has atwo-part sleeve 8 with an inner sleeve 8′ and an outer sleeve 8″. Theinner sleeve 8′ is arranged on an exposed end portion 10 of the opticalfiber 2 and closely encloses the optical fiber 2 in this exposed endportion. The inner sleeve 8 has an outside diameter which correspondsapproximately to that of a sheathing 12, by which the optical fiber 2 isotherwise surrounded.

The outer sleeve 8″ is arranged with a front sleeve portion 22 on theinner sleeve 8′ and extends with a rear sleeve portion 20 part way overthe part of the optical fiber 2 that is surrounded by the sheathing 12,adjoining the exposed portion 10 of the optical fiber 2. The outersleeve 8″ is, furthermore, firmly fixed on the inner sleeve 8,preferably by means of an adhesive agent. The inner sleeve 8′ and theouter sleeve 8″ are preferably made of the same material, in particularof a material which has a coefficient of thermal expansion correspondingto the optical fiber 2.

The inner sleeve 8′ and the outer sleeve 8″ terminate flush with theextreme end 14 on the right in FIG. 7a of the optical fiber 2, so thaton the associated extreme end there is formed a continuous, planarcoupling face 16, with which the optical fiber coupling unit 1 can beplaced against a placement face on an optical waveguide component, inorder to couple the optical fiber 2 optically to this optical waveguidecomponent.

Both the outer sleeve 8″ and the inner sleeve 8′ are provided in thepresent case as closed sleeve parts and consequently extenduninterruptedly around the optical fiber 2. However, in a waycorresponding to the embodiment according to FIGS. 6a, 6 b, the outersleeve 8″ may also be provided in its rear sleeve portion 20, remotefrom the one extreme end 14 of the optical fiber 2, with a transverseslit, in which the optical fiber 2 together with its sheathing 12 isaccommodated and bonded in place.

The outer sleeve B″ serves for the optical fiber 2 as tension relief andas protection against buckling, in order to prevent buckling of theoptical fiber 2 at the location at which it leaves the inner sleeve 8′.

Commercially available capillaries or ferrules with a constant insidediameter are used with preference as the outer sleeve 8″ and as theinner sleeve 8′. The embodiment consequently has the advantage overthose according to FIGS. 5a, 5 b and 6 a, 6 b that it can be realized atlower cost, since the sleeve 8 can be put together just from standardcomponents.

The outside diameter of the inner sleeve 8′ may also be different fromthe outside diameter of the sheathing 12. If in this case an outersleeve with a constant inside diameter, which is adapted to the greateroutside diameter of either the sheathing 12 or the inner sleeve 8′ isused, an intermediate space present as a result between the sheathing 12or the inner sleeve 8′ and the inner wall of the outer sleeve can befilled with a filler, for example an adhesive agent.

FIG. 7b shows the optical fiber coupling unit from FIG. 7a in a viewfrom the front, i.e. in a view from the right in FIG. 7a. The opticalfiber 2, the inner sleeve 8′ and the outer sleeve 8′, which are arrangedconcentrically with respect to each other and with respect to theoptical fiber 2, can be seen from this.

In the exemplary embodiments, a sleeve 8 with a circular-cylindricalouter shape and circular-cylindrical inner shape for accommodating theexposed optical fiber 2 has been described. The sleeve 8 may also have adifferent outer cross section and a different inner cross section, forexample it may have an oval or angular cross section on the outsideand/or inside.

In the case of the exemplary embodiments described, the optical fiber 2and the sleeve 8 are arranged concentrically with respect to each other.Although this concentric arrangement is preferred, the optical fiber 2may also be arranged offset from the longitudinal axis of the sleeve 8.

In FIG. 8, an optical waveguide arrangement 50 according to theembodiment of the invention is represented. The optical waveguidearrangement 50 has an optical chip 52, on which there is provided aplanar placement face 54, from which there extends an optical structure56, which opens out with one end at the placement face 54. Thearrangement 50 has, furthermore, an optical fiber coupling unit 1according to the invention, which is placed with its coupling face 16against the placement face 16 of the optical chip 52, therebyestablishing an optical coupling between its optical fiber 2 and theoptical structure 56, and is fastened on said placement face, inparticular bonded in place. The adhesive is preferably applied here tothe entire coupling face 16, so that the extreme end 14 of the opticalfiber 2 is also covered.

In the present case, the coupling face 16 and the placement face 54 arein each case designed as sloping faces, which are respectively inclinedat an angle of 82 degrees with respect to the longitudinal axis of theoptical fiber 2. The coupling face 16 and the placement face 54 runparallel to each other, the optical fiber 2 being aligned in itslongitudinal direction with the end portion 58 toward it of the opticalstructure 56.

What is claimed is:
 1. An optical fiber coupling unit comprising: anoptical fiber and a sleeve, wherein the optical fiber has a sheathing,and the end portion of the optical fiber is accommodated in the sleeveand has a portion of the sheathing removed, the sleeve furthercomprising an inner sleeve and an outer sleeve, the inner sleeve beingarranged on the end portion of the optical fiber, and the outer sleeveextending with a sleeve portion remote from the one extreme end of theoptical fiber over a port ion of the sheathing and having about the sameoutside diameter as the sheathing, and the outer sleeve having a planarsurface adjacent to its circumferential surface and an end face, thesleeve being arranged on an end portion of the optical fiber with theend face terminating flush with an end of the optical fiber, therebyforming a continuous coupling face so that the optical fiber couplingunit can be placed onto an optical waveguide component to establish anoptical coupling.
 2. The optical fiber coupling unit according to claim1, the optical fiber being surrounded by the sleeve with a distancebetween the optical fiber and the inner wall of the sleeve being about1-5 μm.
 3. The optical fiber coupling unit according to claim 1, whereinthe optical fiber is bonded to the sleeve using an adhesive.
 4. Theoptical fiber coupling unit according to claim 1, wherein the continuouscoupling face extends at an angle of about 82 degrees with respect to alongitudinal axis of the optical fiber.
 5. The optical fiber couplingunit according to claim 1, wherein the sleeve is made of a materialhaving a coefficient of thermal expansion corresponding to about that ofthe optical fiber.
 6. The optical fiber coupling unit according to claim1, wherein the sleeve is made of a material selected from the group of aglass and a ceramic.
 7. The optical fiber coupling unit according toclaim 1, wherein the sleeve has an outside diameter between about 2 mmand about 10 mm.
 8. The optical fiber coupling unit according to claim1, the planar surface extending to the continuous coupling face.
 9. Theoptical fiber coupling unit according to claim 1, the sleeve having asleeve portion remote from the end of the optical fiber that surrounds aportion of the sheathing, a distance between the sheathing and the innerwall of the sleeve being about 1-5 μm.
 10. The optical fiber couplingunit according to claim 9, the sleeve being transversely slit in itssleeve portion remote from the end of the optical fiber, thereby forminga slit space with a portion of the optical fiber having its sheathingbeing arranged in the slit space.
 11. The optical fiber coupling unitaccording to claim 1, the inner sleeve being bonded to the outer sleevewith an adhesive.
 12. The optical fiber coupling unit according to claim1, the sleeve having a length of at least about 2 mm.
 13. An opticalwaveguide arrangement comprising an optical waveguide component, saidoptical waveguide component having a placement face, from which anoptical structure extends, and an optical fiber coupling unit, theoptical fiber coupling unit comprising a sleeve having a longitudinallength with an optical fiber attached thereto, the optical fibercoupling unit having a partial circumferential surface adjacent to aplanar surface, wherein the planar surface bisects the partialcircumferential surf ace along a majority of the longitudinal length ofthe sleeve with a coupling face on an end portion of the sleeve, theoptical fiber coupling unit being attached so that its coupling face isadjacent to the placement face of the optical waveguide component,thereby establishing an optical coupling between the optical fiber andthe optical structure.
 14. An optical fiber coupling unit comprising anoptical fiber and a sleeve, the sleeve having a first end, a planarsurface, a partial circumferential surface, and a coupling end, whereinthe planar surface extends from the coupling end to the first end; thesleeve being arranged on an end portion of the optical fiber and withthe coupling end terminating flush with an end of the optical fiber,thereby forming a continuous coupling face so that the optical fibercoupling unit can be placed onto an optical waveguide component toestablish an optical coupling.
 15. The optical fiber coupling unitaccording to claim 14, wherein the planar surface is disposed at anangle with respect to the continuous coupling face.
 16. The opticalfiber coupling unit according to claim 14, wherein the planar surface isdisposed at an angle of about 82 degrees with respect to the continuouscoupling face.
 17. An optical waveguide arrangement comprising anoptical waveguide component, said optical waveguide component having aplacement face, from which an optical structure extends, and an opticalfiber coupling unit comprising a sleeve with an optical fiber attachedthereto, the sleeve having a first end, a planar surface, a partialcircumferential surface, and a coupling end, wherein the planar surfaceextends from the coupling end to the first end, wherein the opticalfiber coupling unit being is attached so that its coupling end isadjacent to the placement face of the optical waveguide component,thereby establishing an optical coupling between the optical fiber andthe optical structure.